Conventionally, in order to minimize dissipation and emission of noise, dust and exhaust gas produced in operation of a steel making electric-arc furnace into atmosphere, a measure is taken to surround the electric-arc furnace wholly with sound insulating and dust-proof panels and thus form a shroud. In the following will now be described the conventional shrouds and the problems involved in such shrouds briefly.
In FIGS. 1 and 2 is shown a conventional shroud 1 as Case 1. In this example, the electric-arc furnace main body 2 is surrounded by a sound insulating wall 3. At the top of this insulating wall 3 are provided rails 4 which are adapted for a truck type sound insulating cover 5 to move thereon. On the top sound insulating cover 5 is fitted a dust collecting elbow 6 which is connected to a dust collector (not shown). Further, a sand seal or other sealing device 8 is provided between the lower end of the side edge 7 of the top sound insulating cover 5 and the top of the sound insulating wall 3. The shroud of such system is disadvantageous in that when the top sound insulating cover 5 is moved, the dust collecting elbow 6 moves together with the top sound insulating cover 5 to a position shown by solid lines and thus separates from a fixed duct 9, making it difficult to collect dust within the shroud. For example, when scraps 11 are charged into the electric-arc furnace with the top sound insulating cover 5 opened and a scrap bucket 10 is introduced into the shroud, the generated dust and gas flow as shown by arrow a into atmosphere through the opening at the top of the shroud.
In FIGS. 3 and 4 is shown another type of the conventional shroud as Case 2. In this example, the shroud 1 surrounding the electric-arc furnace 2 has a dust collecting duct 12 provided at the top and an opening extending on a side wall 13 and a top wall 14, said opening having a width enough to introduce a scrap bucket (not shown) into the shroud 1. A semi-portal door 15 for covering the opening is provided so as to be movable sideward to a position shown by two-dot chain line in FIG. 4. The shroud of this system has said semi-portal door 15 kept opened when scraps are introduced into the furnace so that generated dust and exhaust gas are dissipated into atmosphere through the opening in the top of the shroud 1.
FIG. 5 shows a still another type of the conventional shroud as Case 3. In this case, the shroud 1 surrounding the electric-arc furnace main body 2 has a dust collecting device 16 provided at the upper part, an opening on the side wall 13 for introduction of the scrap bucket and doors 15' covering said opening, and another opening 18 in the top wall 14 for passage of a rope 17 suspending said bucket and a panel 19 to open or close said opening 18. Further, near said opening 18, an air curtain device 20 is provided to take, when said panel 19 is opened, the flow of exhaust gas generated in the direction of arrow a from the furnace when scraps are charged in the direction of arrow c, discharge the same in the direction of arrow d and deflect it along a tilted flange 21 to the inlet port 22 of the dust collecting device 16. This system has a good efficiency of discharge of the exhaust gas in that the air curtain device 20 does not take in the external air. But, the exhaust gas generated at the time of oxygen blow is of high temperature. Further, when the furnace cover is opened for additional charge of scraps, the upper part of the shroud is exposed to a very high temperature of the heat of radiation of the molten metal in the electric-arc furnace. Accordingly, it is required to take measures for prevention of damage due to dielectric breakdown and thermal deformation of the motor and fan of the air curtain device 20. Further, because of intake of the exhaust gas containing dust in a great quantity, the fan impeller is subject to wear, resulting in unbalanced vibration and in turn damage to the fan.
In FIGS. 6 and 7 is shown a further conventional shroud as Case 4. In this case, the shroud 1 surrounding the electric-arc furnace 2 is provided at the upper part thereof a suction port 22 which is connected to a dust collecting device, an opening extending on the side wall 13 and the top wall 14 for introduction of a scrap bucket (not shown), and two semi-portal doors 15 covering said openings respectively and being adapted to move sideward to positions shown by two-dot chain line in FIG. 7. Further, there are provided, at the top of each door 15, a spacing 24 allowing to pass a scrap bucket suspending rope (not shown) when the door 15 is closed, and an air curtain device 20 to seal said spacing 24 and thus allow air to flow in the direction of arrow d across the spacing 24. Primarily, the air curtain should operate only for several minutes during which scraps are charged. But, according to this system, the spacing 24 allowing to pass the rope is kept open during the process of smelting when the furnace cover 25 and doors 15 are closed so that it is required to operate the air curtain constantly, and such is useless. Further, in order to seal the exhaust gas produced in a great quantity when scraps are charged additionally, the air curtain of the air push system fails to provide a satisfactory effect.
The present invention is intended to provide a shroud of steel making electric-arc furnace which solves the problems in the above-mentioned conventional shrouds and is capable of reducing the dissipation into atmosphere of the exhaust gas at the time of scrap charging to minimum and prevent dissipation of the exhaust gas in operation of the furnace without any particular powered air curtain device provided.
The present invention will now be described in details with reference to embodiments represented in the accompanying drawings.